Wireless personal area networks (“WPANs”) are used to convey information over relatively short distances. Unlike wireless local area networks (“WLANs”), WPANs need little or no infrastructure, and WPANS allow small, power-efficient, and inexpensive solutions to be implemented for a wide range of devices. Smart Utility Networks (“SUNs”) may operate either over short ranges such as in a mesh network where utility meter information is sent from one utility meter to another or over longer ranges such as in a star topology where utility meter information is sent to a poletop collection point. The terms WPAN and SUN are used interchangeably in this document.
For a packet-based OFDM system, a preamble is provided at the start of the packet. In some systems, the preamble is referred as synchronization header. Usually, the preamble (synchronization header) consists of two parts referred to short training field (STF) and long training field (LTF). STF allows automatic gain control AGC, packet detection, fractional frequency offset estimation, and coarse synchronization and LTF allows integer frequency offset estimation, fine synchronization, fine frequency offset estimation, and channel estimation.
The quality of LTF impacts the system performance because it determines the quality of the channel estimation and the fine frequency offset estimation. The quality measure of the signal is SNR. Thus, it is important to process LTF without hurting its inherent SNR. In the LTF, a doubled cyclic prefix CP is provided to give robustness to inaccuracy in fast Fourier transform FFT timing placement.